Good question, and a learning experience for me

I missed it too, not realizing that the underscore wouldn't catch 'C_us'. The lesson learned is that underscore as a wildcard means that there MUST be some character, but % will accept the absence of a character. Proved this out by modifying your question a touch.

create table #Like_Test( Col1 varchar(5) )

go

insert #Like_Test values('_Cu')

insert #Like_Test values('_Cus')

insert #Like_Test values('Cus_')

insert #Like_Test values('C_us')

insert #Like_Test values('Cus')

insert #Like_Test values('Cu_s')

select * from #Like_Test

where Col1 Like '%Cu_%'

select * from #Like_Test

where Col1 Like '%Cu%'

select * from #Like_Test

where Col1 Like '%C%u%'

drop table #like_test